The invention relates to novel nylon compositions, a process for their manufacture and their use as structural and decorative articles that maintain their appearance upon weathering in the presence of UV light.
Ultraviolet light of wavelengths between 280 nm and 400 nm is known to degrade exposed organic matter. Materials used in exterior applications and interior applications (where there is exposure to UV rays through glass) such as fibers and fabrics for use in applications including marine sails and ropes, awnings, tents, flags, upholstery (including interior automotive fabrics), carpet, sports equipment, soft-sided luggage, seatbelt webbing, animal control webbing and clothing!, molded plastic parts for use in applications including automobile parts (such as mirror housings, door handles, body panels, roof rack components, cowlings, wheel covers, windshield wiper components, window trim parts, and bumpers), as well as, sports equipment, tool housings, lawn equipment housings, lawn mower decks, lawn furniture, furniture components, carriages, baskets and toys!, rotationally molded articles such as tanks, tubes, kayaks, and hollow consumer products!, plastic films for applications including agricultural applications (such as greenhouse coverings, crop protection and food packaging), packaging for chemical products (such as pesticides and fertilizers)!, and plastic coatings for applications including paint! are susceptible to photochemical degradation. Exterior weathering and accelerated weathering simulations also expose plastics to rain, moisture, condensation, and heating/cooling cycles. These conditions are well known to exacerbate the loss of properties of UV exposed plastic materials. A review of the important variables in material weathering can be found in, G. Wypych, "Handbook of Material Weathering", ChemTech Publishing, Toronto, 1995.
Weathered polymers develop undesirable color or haze and subsequently lose their transparency and physical properties such as tensile strength, flexibility, gloss, and impact resistance. Dyed, pigmented, and mineral and glass filled plastics, and textiles (e.g., carpet fibers), and color containing plastics e.g. aliphatic and aromatic polyamides including nylon 6, nylon 11, nylon 12, nylon 6,12, nylon 6,10, nylon 6,9 and nylon 6,6; polycarbonate; polyesters such as poly(ethyleneterephthalate) (PET) and poly(butyleneterephthalate) (PBT); polyolefins such as poly(ethylene), poly(propylene); aramids; acrylates; acetates; polyvinylchloride; polyimides; fluoropolymers; polyurethanes; polyacetals; polysulfones and polyaryletherketones, as well as copolymer blends (such as impact modified nylon, and PBT/PET! fade, shift in tone, become brittle, lose their elasticity and eventually completely deteriorate.
As a result, the plastics industry has developed a broad range of stabilizers to prevent UV degradation. These include, radical scavengers such as hindered amine light stabilizers (HALS), phosphites and phenolic antioxidants (AOs), thioethers, metal dithiolates, sulfoxides, among others and ultraviolet light absorbers such as benzotriazoles (BZTs), hydroxybenzophenones (HBPs), cinnamates, benzylidene malonates and nickel chelates. A broad review of these and other stabilizers can be found in J. F. Rabek, "Photostabilization of Polymers; Principles and Applications", Elsevier Applied Science, NY, 1990.
U.S. Pat. No. 5,216,103 ('103 patent) to Enichem Synthesis S.p.A. discloses a silicone-based UV stabilizer that may be used with polyamides. The silicone-based stabilizer of Enichem contains a reactive organic group (which may react with the polyamide resin) and a sterically hindered pipiridine (HALS) group. The reactive groups are incorporated into the silicone to render the hindered amines unextractable for uses such as food contact films. The siloxane component of the '103 patent serves essentially as a carrier for the hindered piperidine. By virtue of the chemical attachment of the hindered amine moiety to the siloxane chain it is difficult to independently vary of the content of HALS and siloxane in the material to be stabilized. Thus, in applications where a siloxane material serves a direct role, the composition can not be easily adjusted to obtain optimal performance.
In order to be useful in the stabilization of polyamides, a composition must: abate the degradation of exposed surfaces by radical and other processes; not add objectionable color to the final composition; be nonvolatile under processing and end use conditions; not decompose under processing and end use conditions; not adversely affect the processability of the polyamide e.g. lubricate an extruder screw, significantly impact the torque of an extruder (either positively or negatively), lessen the throughput of an extruder, or slow the cycle time in injection molding!; not "bloom" excessively in processing or end use (e.g., leave a residue on a mold of an injection molding machine); and must not give off any objectionable odors during processing.
While the prior art describes compositions which may give some intermediate improvements in the weathering stability of polymers, significant improvements are necessary to enable nylon materials to retain their properties and appearances under prolonged exterior weathering.